1. Field of the Invention
The invention relates to methods, and related apparatus, for controlling processing entities used, for instance, in communication systems such as for the control of signalling traffic between a signalling gateway and a plurality of application server processes.
2. Background Art
Establishing connections between two telephones involves a complex interaction of digital messages, hereinafter referred to generally as signalling. Nowadays telephone systems perform what is known as “out-of-band” signalling. Out-of-band signalling means that the communications required between the switches and other equipment in the network take place on communication channels other than the channel by which the voice or data flows. Typically, the out-of-band signalling takes place by means of digital communication channels. Thus, the public switch telephone network (PSTN) generally uses two types of channels, media and signalling.
Several protocols have been defined for out-of-band signalling. The most commonly used protocol, in North America, Asia and Europe, is known as Signalling System No. 7 (SS7). However, the SS7 protocol defines more: than just a protocol for communication between switches. It also defines an entire switching network for facilitating signalling for call establishment, routing, and information exchange functions of switched circuit networks.
Since the amount of data transferred over data networks is now much larger than the voice traffic that is carried over the PSTN, carriers are in the process of consolidating both types of networks. In addition, telecommunication networks are increasingly making use of standard computing hardware in order to reduce IT costs.
Therefore, there is a trend in the telephone industry to migrate telephone systems using SS7-based networks for signalling to Internet Protocol (IP) networks. The Internet protocols are standardised by the Internet Engineering Task Force (IETF). Moving either or both of the media and signalling channels to an IP infrastructure involves the use of very different technologies and can be done independently. The SIGTRAN IETF working group is currently in the process of defining the protocols for back-hauling SS7 signalling messages across IP networks. Generally speaking, signalling across an IP network involves replacing the lower levels of the SS7 layered protocol communications and transport layers with IP network protocol communications and transport layers.
The SIGTRAN group have taken the initiative to define open standards for transporting SS7 over IP networks. With SIGTRAN technology, telephone services which today lie on top of SS7 networks, can run Application Servers (ASs) lying on top of IP networks. The interworking with SS7 networks is performed by SIGTRAN signalling gateways (SGs).
For additional information regarding SS7 network switching over IP networks, reference may be made to the (IETF) working drafts “Signalling Connecting Control Part User Adaptation Layer (SUA)” available from the IETF website at www.ietforg, and IETF RFC 3332 “SS7 MTP3—User Adaptation Layer (M3UA)”, available from the IETF website, and which are both incorporated herein by reference as if reproduced in full. It is noted that the SUA document is a work in progress and is therefore subject to, change. However, these documents, which will be referred to herein as the SIGRAN documents, exemplify the changes necessary to a standard SS7 signalling system for its implementation in an IP network context. As well as defining the functions of signalling gateways and signalling gateway processes, the SIGTRAN documents referred to above specify in detail the protocols to be implemented between a signalling gateway and a application server.
For more general background information regarding SIGTRAN protocols, reference may be made to the International Engineering Consortium, in document “SS7 Over IP Signalling Transport and SCTP,” which is available from the IEC website www.iec.org, and which is incorporated herein by reference as if reproduced in full.
To enhance the availability of the signalling gateway, it can be distributed over several processes running in one or several computers, each of them being a Signalling Gateway Process (SGP). Every SGP belonging to a particular SG has the same SS7 point code (or the same list of PCs), with each SGP generally being connected to the SS7 network through redundant links that are selected in conventional manner via Signalling Link Selector (SLS) values present in the SS7 messages.
On the IP network side, each SGP is connected to the ASPs running the services. Each AS, which can typically be identified with a single logical service, such as a Short Message Service Centre (SMSC), can also be implemented in a distributed manner by one or more processes or computers—referred to as the ASPs. To provide improved reliability, each SGP is typically directly connected to each ASP through an Stream Control Transfer Protocol (SCTP) association such that there is one association between each SGP and each ASP.
However, the use of redundant links to the SS7 network, which is highly desirable to ensure fault tolerance of the gateway, can result in latency and performance inefficiencies within the gateway since signalling messages may need to be transmitted between elements of the gateway itself in order to reach signalling unit hardware which carries an outbound SS7 link selected in accordance with an SLS value of a message.
It is an object of the present invention to overcome this and/or other drawbacks with the prior art.